The present invention relates to a water-cooled diesel engine for use as an outboard engine.
Hitherto, 2-cycle gasoline engines operable with a fuel mixture have been used most popularly as marine outboard engines mounted on the stern of small-sized vessels, because this type of engine best meets the requirements for light weight and small size which are the essential requisites for marine outboard engines. Thus, diesel engines have been used very seldom as marine outboard engines. The current rise in the price of gas fuel, however, has given a rise to the demand for use of diesel engines as marine outboard engines.
The use of a diesel engine as a marine outboard engine, however, poses various problems. Namely, a diesel engine can produce only a comparatively small power per unit weight because of its heavy weight due to the use of cast iron as the material of the cylinder block and cylinder head. In addition, the number of parts is considerably large because the cylinder block and the cylinder head are constructed separately from each other and jointed to each other by means of bolts with a gasket interposed therebetween. In addition, the seal of the gasket tends to become imperfect.
An outboard engine has to be swung manually for steering and has to be tilted up as desired. In addition, such an engine has to be transported and mounted easily. Furthermore, an outboard engine is required to have a centroid on the neutral axis thereof. Namely, if the centroid is offset to the left or right, the maneuverability of the engine will be impaired unfavorably.
In order to obviate these problems, it is necessary to meet the requirements such as minimized weight of the outboard engine unit including the engine itself, symmetry of the outboard engine with respect to the plane parallel to the running direction, minimized height, compactness of the outboard engine, reduction in the number of the parts, simplified construction and reduced cost.
However, when a diesel engine is used as a marine outboard engine, the compactness of the engine is affected by the position of the exhaust gas outlet.